Cellulosic sheet material having a thermosetting resin bonder and a surfactant debonder and method for producing same

ABSTRACT

Cellulosic sheet materials having an improved ratio of wet tensile strength to dry tensile strength comprise cellulosic fibers; at least one debonder selected from the group consisting of anionic and cationic surface active agents; and a cationic thermosetting resin such as those normally employed to increase the wet strength of paper.

United States Patent [1 1 Freimark et a1.

[451 Aug. 28, 1973 CELLULOSIC SHEET MATERIAL HAVING A THERMOSETTING RESIN BONDER AND A SURFACTANT DEBONDER AND METHOD FOR PRODUCING SAME Inventors: Bernard Freimark, Claymont, Del.; Richard W. Schaftlein, Chadds Ford,

Assignees Scott Paper Company, Philadelphia,

Filed: Oct. 13, 1971 Appl. No.: 189,045

U.S. Cl 260/l7.3, 162/157 C, 162/166,

162/167 Int. Cl. C08g 51/18, D2ld 3/00 Field of Search 260/173; 162/166,

[56] References Cited UNITED STATES PATENTS 2,683,087 6/1954 Reynolds l 162/166 3,210,239 10/1965 Eberl et a1. 162/166 3,554,863 l/197l Hervey et a1. 162/158 2,683,089 7/1954 Reynolds 162/166 Primary Examiner-William H. Short Assistant Examiner-Edward Woodberry Attorney-John A. Weygandt, William J. Foley et a1.

[5 7] ABSTRACT 6 Claims, No Drawings CELLULOSIC SHEET MATERIAL HAVING A THERMOSETTING RESIN BONDER AND A SURFACTANT DEBONDER AND METHOD FOR PRODUCING SAME BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to improved cellulosic sheet materials and to a method of preparing said materials. More particularly, the invention relates to cellulosic sheet materials prepared from a furnish comprising cellulosic fibers; at least one debonder selected from the group consisting of anionic and cationic surface active agents; and a cationic thermosetting resin such as those normally employed to increase the wet strength of paper.

2. Description of the Prior Art The production of sheet materials from cellulosic fibers generally begins with an aqueous slurry of the fibers, said slurry being commonly referred to as a furnish. In the preparation of sheet material, the furnish is cast onto a wire surface so that the water is removed and the fibers brought into close contact with one another. When dried in this close contact, hydrogen bonds are formed between the hydroxylgroups of the fibers resulting in the production of a sheet material, the strength of which is due to this natural fiber-to-fiber bonding. When the dry sheet is rewet, these hydrogen bonds are broken and the paper loses most of its strength.

To prevent this strength loss, various chemical treatments have been employed. Among the most successful treatments is the use of synthetic resins which, when added to the cellulosic fibers, either before or after the sheet is formed therefrom, and cured or polymerized, can significantly increase the wet strength of the sheet. Most commonly used are the urea-formaldehyde and melamine-formaldehyde type resins. These resins are referred to as being substantive with respect to cellulosic fibers, because-they are cationic and are, therefore, easily deposited on, and retained by, the anionic paper-making fibers. However, the addition of these resins to a paper-making furnish results not only in the preparation of sheets having increased and improved wet tensile strength but also results in a stiffer, harsher sheet.

The production of a stiffer sheet is often due, at least in part, to an increase in the dry tensile strength of the sheet. For certain applications such as tissues, paper towels and other sanitary paper products, an increase in the stiffness and dry tensile strength of the sheet is undesirable and it would be advantageous to be able to increase the wet tensile strength of the sheet without simultaneously increasing the dry tensile strength and,

therefore, the harshness of the sheet.

Certain chemical additives, commonly referred to as debonding agents, when added to a paper-making furnish are known to interfere with the natural fiber-tofiber bonding which occurs during the sheet forming and drying operation. However, it has not heretofore been known that these debonding agents, when added with the cationic thermosetting resins described above, would produce cellulosic sheet materials having the desired properties of significantly increased wet tensile strength without a comparable increase in either the dry tensile strength or the harshness of the sheet.

SUMMARY or THE INVENTION In accordance with the present invention, soft, cellulosic sheet materials having an improved ratio of wet tensile strength to dry tensile strength are prepared comprising cellulosic fibers; at least one debonder selected from the group consisting of anionic and cationic surface active agents; and a cationic thermosetting resin such as those normally employed in the prep- 0 aration of wet strength papers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In carrying out the present invention as aqueous slurry of cellulosic fibers is prepared according to any of the well-known methods. This aqueous slurry, or furnish, is then treated with chemicals in the beater, stockchest, fan-pump, heatbox or at any other suitable point ahead of the Fourdrinier wire, or sheet-forming stage. Cellulosic fibers which have been found to be especially useful in carrying out the present invention include wood pulp fibers and mixtures of wood pulp and synthetic fibers such as rayon.

The chemical treatment comprises at least one resin and one debonder, as hereinafter defined. After the chemical treatment, sheets are prepared from the furnish according to any well-known method.

The various chemical additives employed in carrying out the present invention can be generally defined as follows:

, Resins The resins which may be employed in carrying out the present invention include the water-soluble, thermosetting, cationic resins well-known in the art for increasing the wet strength of cellulosic sheet material and including, for example, urea-formaldehyde, melamine-formaldehyde, polyureide-formaldehyde, glyoxal-acrylamide, and polyamide-epichlorohydrin resins. The amount of polymeric compound added can be varied over a wide range depending upon the type of pulp employed, properties desired in the final product, other chemicals added, etc. It has been found that the most satisfactory results are achieved when the resin is added in an amount equal to from about 0.1% to about 4.0% of the bone dry weight of the fibers, and it is especially preferred to add this amount of the resin. Debonders The debonders which can'be employed in carrying out the present invention include anionic and cationic surface active agents. Especially preferred are cationic quaternary ammonium compounds including compounds, such as Velvetol 2000 and Velvetol CI-IR high molecular weight quaternized imidazolines, available from Quaker Chemical Corporation, Conshohocken,

.Pa. Other preferred cationic quaternary ammonium compounds are the alkyl ammonium salts such as dihydrogenated tallow dimethyl ammonium chloride, available from General Mills, Inc., Chemical Division, Kankakee, Illinois as Aliquat H226; dialkyl amide diethyl ammonium sulfate, available from Ryco, Inc., Conshohocken, Pa. as Rycofax 618; and Rycofax 637, and Amphoteric quaternary ammonium compound also available from Ryco, Inc.

Anionicsurface active agents which are also useful as debonders in carrying out the present invention include compounds such as sodium tetradecyl sulfate available as Tergitol Anionic 4 from Union Carbide Corporation,

New York,'New York and the sodium salt of sulfated nonyl phenoxy poly (ethyleneoxy) ethanol available as Alipal A3436 from General Aniline and Film Corporation, New York, New York.

The amount of debonder employed can be varied over a wide range depending upon the furnish employed, the properties desired in the final product and other variables associated with the sheet-forming and drying operation. it is especially preferred to employ an amount of debonder equal to up to about 1.5% of the bone dry weight of the fibers employed. The debonder may be added to the furnish either before or after the resin.

In order to describe the present invention so that it may be more clearly understood, the following examples are set forth in which all percentages of chemical additives are based on the bone dry weight of the pulp employed. Physical properties reported herein were obtained using the following test procedures, except as otherwise noted in the examples.

Basesheets were prepared on a typical Fourdrinier machine.

Basis weight of the sheets was determined by weighing eight sheets measuring 2% inches X 2% inches and converting the result to pounds/ream (2,880 square feet).

Dry tensile strength was determined with a standard lnstron Tensile Tester using 1 inch wide test strips and the procedure described in TAPPl Standard T404ts- 606.

Wet tensile strength was determined as for dry tensile strength following the procedure described in TAPPI Standard T456os-68.

Fold value and crush value were measured on an apparatus designed to give an indication of the softness of a sheet by measuring the force required to fold the sheet (the fold value) and the force required to crush the folded sheet (the crush value). A decrease in these values is indicative of a softer sheet. The apparatus employed to obtain these measurements comprises an inner set of circular platens and an outer set of annular platens. The platens are arranged so that there is an upper and lower member of each set. The upper circular platen has a diameter of 1.09 inches and a rounded edge having a radius of 0.062 inches. The lower circular platen has a diameter of 1.43 inches and is located directly below the upper circular platen. The upper annular platen has an inside diameter of 2.125 inches and a rounded inner edge also having a radius of 0.062 inches. The lower annular platen is of similar size and is located directly below the upper annular platen. The rounded edges of the two sets of platens are separated by a distance of 0.382 inches. The upper member of each set of platens is attached to means for clamping that set of platens together and the surface of all the platens are highly polished.

There is also included, below the space between the two sets of platens a circumferential ring attached to means for moving said ring through said space. The ring has an inner diameter of 1.5 inches, an outer diameter of 1.75 inches and the rounded portion has a radius of 0.062 inches. Above the space is another annular platen having an inside diameter of 1.16 inches and an outside diameter of 2.062 inches. This platen is also highly polished and is attached to means for moving said platen towards the space.

In operation the sheet to be tested is placed between the upper and lower members of the two sets of platens. The inner circular set of platens is clamped to hold the sheet in place and the distance between the upper and lower members of the outer annular set is adjusted to 0.065 inches. The distance the circumferential ring will travel is adjusted to 0.250 inches and a force is applied to said ring causing it to move in an upward direction through that distance folding the sheet as it moves. The maximum force on the ring during this folding operation is recorded in grams and is referred to as the fold value of the sheet.

After the sheet is thus folded the outer annuler set of platens is clamped to maintain the sheet in the folded condition. The folded sheet is crushed by, simultaneously, moving the circumferential ring down away from the sheet and moving the annular platen down onto the sheet for a distance of 0.050 inches. The maximum force on the platen as it moves through this distance is measured in grams and is referred to as the crush value of the sheet.

In the examples the softness of the sheet is indicated by the sum of the fold and crush values.

Sheets produced in accordance with the present invention are characterized by their improved ratio of wet tensile strength to dry tensile strength and their softness. These sheets are useful in sanitary products such as tissues and paper towels.

The following examples are set forth primarily for the purpose of illustration, and any specific enumeration of detail contained therein should be interpreted as'a limitation on the concept of this invention.

EXAMPLE I A wood pulp slurry was prepared comprising bleached northern Kraft softwood and 30% bleached southern Kraft hardwood. The slurry was divided into two portions. To one portion there was added l.0%, based on the bone dry weight of the fiber present in said furnish, of a cationic urea-formaldehyde resin prepared in accordance with the procedure described in U.S. Pat. No. 3,275,605 issued on Sept. 27, i966, to Eastes et al. and having a nonvolatile solids content of from about 27% to about 30%, and 0.3%, also based on the bone dry weight of the fibers, of Velvetol HS, a high molecular weight quaternized imidazoline available from Quaker Chemical Corporation, Conshohocken,

Pa. When tested, as described above, basesheets prepared from a sample of this furnish had the following physical properties:

Basis weight (lbs/ream)30.6

Wet tensile strength (oz/in.) l0.l Dry tensile strength (oz/in.)22.5

Wet tensile strength/dry tensile strength-44.8%

Fold and Crush (grams)-636 By comparison, basesheets prepared from a sample of the furnish containing l.0% of the urea-formaldehyde resin but no debonder had the following physical properties:

Basis weight (lbs/ream)-30.5

Wet tensile strength (oz/in.)8.9

Dry tensile strength (oz/in.)-37.3

Wet tensile strength/dry tensile strength23.9%

Fold and Crush (grams)l,092

EXAMPLE ll A wood pulp slurry was prepared as in EXAMPLE I.

To a sample of the slurry there was added 1.0%, based on the bone dry weight of the fibers in said slurry, of a cationic urea-formaldehyde resin also prepared as in US. Pat. No. 3,275,605 referred to above and having a nonvolatile solids content of about 23% and a higher molecular weight than the resin employed in Example I, and 0.3% Velvetol HS, a high molecular weight quaternized imidazoline available from Quaker Chemical Corporation, Conshohocken, Pa. Basesheets prepared from this furnish had the following physical properties:

Basis weight (lbs/ream)30.1

Wet tensile strength (oz/in.)l0.6

Dry tensile strength (oz/in.)-23.5

Wet tensile strength/dry tensile strength45.3%

Fold and Crush (grams)564 By comparison, basesheets prepared from the same furnish containing only 1.0% of the urea-formaldehyde resin had the following physical properties:

Basis weight (lbs/ream)-31.0

Wet tensile strength (oz/in.)18.3

Dry tensile strength (oz/in.)70.5

Wet tensile strength/dry tensile strength-25.9%

Fold and Crush (grams)l,500

EXAMPLE III A wood pulp slurry was prepared as in Example I. To a first sample of the slurry, there was added 3.0% of the cationic urea-formaldehyde resin described in Example [1 and 0.6% Velvetol HS. Basesheets prepared from a sample of this furnish had the following physical properties:

Basis weight (lbs/ream)30.1

Wet tensile strength (oz/in.)2l.l

Dry tensile strength (oz/in.)42.6

Wet tensile strength/dry tensile strength49.5%

Fold and Crush (grams)779 By comparison basesheets prepared from a second sample of the furnish and containing 3.0% of the ureaformaldehyde resin and no debonder had the following physical properties:

Basis weight (1bs/ream)31.2

Wet tensile strength (oz/in.)27.2

Dry tensile strength (oz/in.)82.2

Wet tensile strength/dry tensile strength33.l%

Fold and Crush (grams)l,600

EXAMPLE IV A wood pulp slurry was prepared as in Example I. To the slurry was added 1.0% of the cationic ureaformaldehyde resin described in Example II. The slurry was divided into several samples each of which was treated with a different amount of Velvetol HS. The results are given in the following table:

TABLE I %Vel- Dry Wet Wet Tensile Fold vetol Tensile Tensile Strength] and HS added Strength Strength Dry Tensile Crush (oz/in.) (oz/in.) Strength 0 70.7 17.8 25.2% 1503 0.05 44.4 19.3 43.1% 1090 0.2 30.9 13.2 42.7% 753 0.3 25.0 10.9 43.6% 710 0.4 30.8 13.9 45.1% 832 EXAMPLE V A wood pulp was prepared as in Example I. To a first sample of the slurry there was added 1.0% of a melamine-formaldehyde resin and 0.2% Velvetol HS. Basesheets prepared from this sample had the following physical properties:

Basis weight (lbs/ream)30.8

Wet tensile strength (oz/in.)l2.5

Dry tensile strength (oz/in.)-33.1

Wet tensile strength/dry tensile strength37.8%

Fold and Crush (grams)1200 By comparison, basesheets prepared from a second sample of the furnish containing only 1.0% of the melamine-formaldehyde resin had the following physical properties:

Basis weight (lbs/ream)30.3

Wet tensile strength (oz/in.)l5 .6

Dry tensile strength (oz/in.)-55.5

Wet tensile strength/dry tensile strength-28.1%

Fold and Crush (grams)-l,300

EXAMPLE VI A wood pulp slurry was prepared as in Example 1. To a first sample of the slurry there was added 1.5% of Parez 63ONC, a glyoxal-acrylamide type resin available from American Cyanamid Corporation and 0.4% Velvetol HS. Basesheets prepared from this furnish had the following physical properties:

Basis weight (lbs/ream)-30.1

Wet tensile strength (oz/in.)6.7

Dry tensile strength (oz/in.)17.9

Wet tensile strength/dry tensile strength-37.4%

Fold and Crush (grams)572 By comparison basesheets prepared from a second sample of the slurry containing 1.5% Parez 63ONC and no debonder had the following physical properties:

Basis weight (lbs/ream)30.3

Wet tensile strength (oz/in.)13.4

Dry tensile strength (oz/in.)-58.2

Wet tensile strength/dry tensile strength23.0%

Fold and Crush (grams)l,l68

EXAMPLE VII A wood pulp slurry was prepared as in Example 1. To a first sample of the slurry there was added 3.0% of the urea-formaldehyde resin described in Example 11 and 0.4% Rycofax 618, a dialkyl amide diethyl ammonium sulfate available from Reichold Chemicals, Inc., White Plains, New York. Basesheets prepared from this furnish had the following physical properties:

Basis weight (lbs/ream)30.1

Wet tensile strength (oz/in)l7.2

Dry tensile strength (oz/in.)34.4

Wet tensile strength/dry tensile strength50.0%

Fold and Vrush (grams)783 By comparison handsheets prepared from a second sample of the slurry and containing only 3.0% of the urea-formaldehyde resin had the following physical properties:

Basis Weight (lbs/ream)3 l .2

Wet tensile strength (oz/in.)27.2

Dry tensile strength (oz/in.)-82.2

Wet tensile strength/dry tensile strength-33.1%

Fold and Crush (grams)l,600

What is claimed is:

1. In a method of producing a cellulosic sheet material utilizing a furnish comprising cellulosic fibers, the improvement which comprises increasing the wet tensile strength to dry tensile strength ratio of the sheet material by including in the furnish at least one debonder selected from the group consisting of anionic surface active agents and cationic quaternary ammonium surface active agents; and a cationic thermosetting resin; in which the amount of the resin in the furnish is equal to from about 0.1% to about 4.0% of the bone dry weight of the fibers employed, and the amount of debonder in the furnish is equal to up to about 1.5% of the bone dry weight of the fibers employed.

2. A method, as claimed in claim 1, in which the resin in the furnish is a cationic urea-formaldehyde resin.

3. A method, as claimed in claim 1, in which the resin in the furnish is a cationic melamine-formaldehyde resin.

4. A method, as claimed in claim 1, in which the cellulosic fibers are wood pulp fibers.

5. A cellulosic sheet material having an improved ratio of wet tensile strength to dry tensile strength comprising cellulosic fibers, at least one debonder selected from the group consisting of anionic surface active agents and cationic quaternary ammonium surface active agents, and at least one cationic thermosetting resin in which the amount of the resin is equal to from about 0.1% to about 4.0% of the bone dry weight of the fibers employed, and the amount of debonder is equal to up to about 1.5% of the bone dry weight of the fibers employed.

6. A cellulosic sheet material, as claimed in claim 5, in which the debonder is a cationic quaternary ammonium surface active agent and the resin is a ureaformaldehyde resin. 

2. A method, as claimed in claim 1, in which the resin in the furnish is a cationic urea-formaldehyde resin.
 3. A method, as claimed in claim 1, in which the resin in the furnish is a cationic melamine-formaldehyde resin.
 4. A method, as claimed in claim 1, in which the cellulosic fibers are wood pulp fibers.
 5. A cellulosic sheet material having an improved ratio of wet tensile strength to dry tensile strength comprising cellulosic fibers, at least one debonder selected from the group consisting of anionic surface active agents and cationic quaternary ammonium surface active agents, and at least one cationic thermosetting resin in which the amount of the resin is equal to from about 0.1% to about 4.0% of the bone dry weight of the fibers employed, and the amount of debonder is equal to up to about 1.5% of the bone dry weight of the fibers employed.
 6. A cellulosic sheet material, as claimed in claim 5, in which the debonder is a cationic quaternary ammonium surface active agent and the resin is a urea-formaldehyde resin. 